1. Field of the Invention
The present invention relates to a method of determining the spring characteristic of a roughing and finishing roll stand and to a method of adjusting the roll gap of the roll stand prior to rolling, particularly for rolling lightweight sections with narrow tolerances, wherein at least one horizontal roll of the stand is adjustable, preferably electromechanically.
2. Description of the Related Art
Roll housings of split construction are known from German Offenlegungsschrift 20 57 960. The roll housings have removable tops and tie rod connections between the housing and the housing tops, wherein the tie rods are mounted so as to be swingable laterally out of the roll stand about axes arranged in the lower housing portion. In addition, the tie rods can be tensioned or pretensioned for the operation of the roll stand by means of hydraulic tensioning units arranged at the heads of the tie rods. The pretensioning pressure continues to act on the tie rod heads during the rolling operation. In this tie rod connection, the hydraulic tensioning unit consists of a cylindrical member which causes the length of extension of the tie rod and of a threaded nut which is subsequently turned further by the length of extension. The pressure medium does not act on the cylindrical member during the operation of the roll stand.
In accordance with a further development disclosed in German Offenlegungsschrift 26 06 842, the pressure medium producing the pretensioning forces can be switched centrally and jointly on and off to the tensioning units of one or more roll stands. Depending on the extent by which the pretensioning pressure is released, the tie rods of one or more roll stands can be swung centrally and jointly by means of the hydraulically acting piston-cylinder units. When the tie rods are swung out of the roll stands, the upper housing tops can be lifted off upwardly. For carrying out the roll exchange, the unit receiving the two horizontal rolls is lifted upwardly and out of the stand by means of a crane arrangement. These measures have the purpose to reduce the time required for the roll exchange and to substantially mechanize the roll exchange.
German Auslegeschrift 12 91 715 discloses a roll stand with open-top housings in which after removal of the housing tops, the chocks of the rolls can be lifted out upwardly. The tops have projections arranged on components which project between the housing columns. The projections engage the upper limiting surfaces of recesses of the aperture sides and can be fixed to the columns by means of tensioning means which act between the projections and the housing columns in direction of the adjusting spindles. The tops can be moved laterally. For this purpose, the housings include a rail arrangement and the tops have drive rollers. When the tops are moved laterally, the stand is open toward the top, so that the roll exchange can be carried out through the open top of the stand. The purpose of these measures is to simplify the roll exchange and to accelerate the roll exchange.
A universal stand with horizontal and vertical rolls in a common vertical axial plane is known from German Offenlegungsschrift 30 39 203. The universal stand includes a frame for the vertical rolls which is closed with respect to the forces being applied. Adjusting spindles for the vertical rolls are mounted in the yokes of the frame. The chocks of the horizontal rolls are supported in pairs in an upper and a lower transverse yoke, wherein the transverse yokes are supported by tension spindles which are axially movably arranged in the frame and the transverse yokes are centrally adjustable relative to the pitch line. The two upper transverse yokes can each be swung out symmetrically laterally relative to the pitch line because the transverse yokes are supported in the swing axis through an extended additional bushing on the tension spindles forming the swing axes. The transverse yokes are swingable so that it is not necessary to provide lifting means, for example, a crane arrangement, for lifting out the transverse yokes. The purpose of this arrangement is to further reduce the roll exchange times.
The above-described roll stands with roll housings of split construction have in common that the different arrangements of the transverse yokes or tops connecting the roll housings make it possible to open the stand quickly at the top so that the roll exchange or the change of the roll sets car be carried out as quickly as possible. None of the references referred to above mention that it is possible with pretensioned open-top stands to roll material within narrow tolerances and with high measuring accuracy only when the expansion behavior of the entire stand including the rolls is known in any selected loading condition and when the rolling mill stand can be exactly adjusted prior to rolling. The speed of the roll exchange is not the only criterion important for the quality of a stand of split construction with housing tops.